The present invention relates to an optical wavelength converter. More particularly, the present invention relates to an optical wavelength converter based on cross-gain modulation with wide input power dynamic range.
Wavelength converters are the key elements in wavelength division multiplexed (WDM) networks and photonic switch blocks. They are the devices that convert the wavelength of optical transmission signals independently of transmission speed and transmission system. One important use is to avoid wavelength blocking in optical cross connects in WDM networks. Therefore, the converters increase the flexibility and the capacity of the network for fixed wavelengths. Among the wavelength conversion methods, cross-gain modulation (XGM), cross-phase modulation (XPM), and four-wave mixing (FWM) in semiconductor optical amplifiers (SOA""s) have been widely studied and investigated. Wavelength converters by XGM in SOA""s have the advantages of simple structure and high conversion efficiency. However, disadvantages include the extinction ratio degradation after conversion, the inversion of bit-stream, and the narrow input power dynamic range.
FIG. 1 shows a diagram for illustrating a conventional optical wavelength converter using cross-gain modulation.
As shown in FIG. 1, the intensity-modulated input signal beam at xcexS and continuous wave beam at xcexC are injected into a semiconductor optical amplifier 13. The input signal beam is the pump beam 15, and the continuous wave beam is the probe beam 16. The intensity of the continuous wave beam, i.e., probe beam 16, depends upon the amount of bias current loaded to the continuous wave source 12 from the current driver 11.
The operation principle relies on gain saturation in the semiconductor optical amplifier 13. A strong pump beam 15 is used to modulate the gain of the semiconductor optical amplifier 13. A probe beam 16 at desired wavelength is modulated according to the bit pattern of the pump beam 15 due to the effect of gain modulation. At the output, the wavelength converted beam is obtained by passing only the probe beam through a band pass filter 14. Therefore, the wavelength of the input signal, xcexS is converted into the desired wavelength, xcexC.
Conventional optical converters using cross-gain modulation have several drawbacks. For example, the extinction ratio of the wavelength converted beam is low and bit stream is inversed. In addition, input power dynamic range is narrow.
The present invention provides an optical wavelength converter based on cross-gain modulation with wide input power dynamic range. An optical wavelength converter based on cross-gain modulation with wide input dynamic range in accordance with the present invention comprises a semiconductor optical amplifier, a continuous wave source, and a probe beam controller. The semiconductor optical amplifier modulates probe power on the basis of pump power. The continuous wave source generates the probe beam and supplies generated probe beam to the semiconductor optical amplifier. The probe beam controller supplies adequate bias current to the continuous wave source and the probe power changes in accordance with the pump power.